Continuous pulping extraction apparatus



Nov. 24, 1964 E. R. BURLING ETAL 3,158,533

cou'rmuous PULPING EXTRACTION APPARATUS Filed Sept. 21, 1962 United States Patent 3,158,533 CONTINUGUS PULPWG EXTRACTIQN APPARATUS Elmer R. Bin-ling, Nashua, and Lawrence A. Carlsmith,

Amherst, NH. (both improved Machinery lino,

Nashua, NIH.)

Filed Sept. 21, 1962, Ser. No. 225,285 12 Claims. (Cl. 162-237) This invention relates to the continuous pulping of fibrous materials, such as wood chips, for example, and more particularly to novel appa atus for extracting separable fluids, either gases or liquids, from wood chips during their treatment while they are moved continuously through a single pressurized upflow reaction vessel. It is a continuation-in-part of Serial No. 28,291, filed May 11, 1960, now abandoned.

The pulping of wood chips or other fibrous material and the like has long been carried out by a succession of treatments which may be summarized as impregnation and possibly preheating of the chips with a liquid to provide a suitable solid particle-liquid mixture; subsequently chemically treating the chips, usually under pressure and for a sbstan-tial period of time; and finally washing the treated chips. Various by-products, both gases and liquids, are produced during the reaction, and with some products, it would be useful to remove a major portion thereof in the early stages of treating. These by-products may include, for example, turpentine, liquid soaps, and various gases.

According to the present invention, novel apparatus is provided whereby such lay-products may largely be extnacted in the early stages of a complete pulping treatment carried out in a single continuous digester. With turpentine, for example, this is important because the yield of turpentine decreases with cooking time as va general rule, apparently because of its destruction by the cooking chemicals. Hence, the best turpentine yields are produced after the heating of the wood chips to be pulped is well advanced, but before substantial cooking has taken place. With gases, they, too, are best removed early in the cooking process since they may have a deleterious effect on subsequent cooking by tending to accelerate the upward chip movement. Soaps and other immiscible liquids, particularly if valuable, should also be removed early to improve their yields, or to prevent their subsequent reaction.

The present invention has accomplished its unique results by the novel combination, with an upflow continuous digester or reaction vessel having a plurality of access openings spaced theroalong, of a separate smaller extraction vessel. Within such vessel, separate liquid and gas phases exist and through it the treating liquid from the digester or reaction vessel is continuously circulated, during which it may undergo a pressure reduction for most efiicient extraction. Means are also provided for controlling the liquid level both within the digester and the extraction vessel, as well as for passing steam through the latter, as an aid to separation, or for heating the circulating liquid. In addition, the digester has mechanical means for advancing the solid particle component, the wood chips, upwardly through it independently of the flow of liquid therein by maintaining a compacted mass of said solid particles extending throughout the effective length of the digester and exerting lifting force directly only on solid particles located at the lower end of the digester, thus ensuring that recirculation for extraction can take place without disturbing the pulping reaction.

For the purpose of fully explaining preferred embodiments of the invention, reference is now made to the following specification, taken together with the accordpanying drawing showing a diagrammatic side elevation of preferred apparatus according to the invention.

Referring to the drawing, the preferred apparatus therein shown is generally similar to the digester or reaction vessel shown in US. Patent No. 2,878,116, issued March 17, 1959, but further includes, according to the present invention, a plurality of liquid access openings preferably opposite one another but which also may be spaced therealong. These openings, some of which are in the form of strainers, are connected to a separate extraction vessel. Means are also provided for controlling liquid flow and level within the extraction vessel, for operating it at a lower pressure than the reaction vessel itself and for removing the various separable liquids therefrom.

More specifically, the apparatus includes a generally cylindrical upright pressure vessel 22 having a bottom opening 18 connected to a suitable input means such as a pump 19 and a top discharge mechanism connected to a suitable pulp storage tank or the like (not shown). The advancing means includes a foraminous screw means mounted for rotational and reciprocatory movement through a limited distance relatively to the length of the vessel within the reaction vessel 22 near the lower end thereof by means of a shaft 30 extending vertically through the bottom of said Vessel generally axially there of. Such forarninous screw means comprises a single turn helical plate 32 having therein a plurality of perforations sufiicient in number to allow substantially free passage of the liquid therethrough but of small enough size to prevent passage of the chips or other fibrous material. Furthermore, the step of such helical surface is closed by a fiat plate at extending vertically between its upper and lower edges, and the peripheral edge thereof is positioned closely adjacent the inner walls of the reaction vessel 22 so that passage of chips into the bottom portion of said reaction vessel 22 may be prevented.

For feeding the pressurized mixture of chips and liquid to the upper surface of said plate, a tubular member 42 having its inner wall concentric with and spaced from shaft 35) is mounted on the lower surface of said helical plate 32 extending downwardly therefrom, thus providing a centralaperture 44. The lower end of shaft 30 extends into a hydraulic cylinder mounted beneath the lower end of reaction vessel 22 and forms the piston thereof, said cylinder being connected to a suitable source of fluid pressure to raise said shaft with the helical plate 32 to reciprocate said plate, the force of the vessel pressure against the area of the upper end of said sharfit being great enough to rapidly lower the plate when the pressure in the cylinder is exhausted, the pressure vessel 22 in such circumstance acts as an accumulator to provide the necessary force at a rapid rate, Furthermore, the volume of a liquid displaced by shaft 30 varies as the shaft reciprochip lifter plate 32 through which liquid may be passed,

a plurality of openings are provided spaced from one another along the length of the vessel. As shown in the drawing five such openings are employed, a lower opening 61, and somewhat higher opening 62 thereabove, intermediate openings 63 and 64 spaced thereabove on oppo site sides of digester 22, an opening 65 spaced somewhat above openings 63 and 64 and an uppermost opening 66. The lower openings 61 and 62 are utilized for heating the Wood chips up to the point of beginning their conversion into pulp, at which time various by-products begin to evolve. Recirculation through these openings is provided by pump 16 and heater 17. The upper opening 66 is in the form of a strainer for controlling the liquid level within the digester, for example.

According to the present invention, either the lower openings 61, 62 or the intermediate openings 63 and 64 are connected to a separate vertically elongated extraction vessel 70 through its lower fluid inlet 71 and upper fluid outlet 72 for recirculation of liquid from the reaction vessel, including heating in substitution for heater 17 if desired. A pump or reducing valve 80 is employed between the lower fluid inlet '71 and the digester opening 63 to aid in such recirculation, such opening 63 being in the form of a strainer. Another pump 81 may be employed between upper fluid inlet 72 and either opening 64 or 65, the desired one of the latter two openings being selected by valve 82. The vessel 74) has a bottom inlet 74 provided with a valve 75 for admitting steam under pressure, and a bottom outlet 73 having a valve 79 for removing high specific gravity liquids. A top outlet 76 is provided for volatile gases, including steam and turpentine, and a somewhat lower upper outlet 38 having a valve 89 is provided for removing low specific gravity liquids.

For controlling the apparatus, a valve 77 is provided at said top outlet 76, such valve preferably being controlled by a level sensing and control device 78 on the extraction vessel to maintain the level of the circulating liquid therein at a substantial distance below the top thereof, preferably at the interface 913 between the circulating liquid and the overlying lower specific gravity liquid 92, although the upper surface of said overlying liquid could also be used. Such level sensing and control devices capable of operating a valve to maintain a liquid level between predetermined limits are well known in the art and need not herein be further described.

In operation the heated liquid containing evolved turpentine in the digester is extracted from the intermediate opening 63, or from lower opening 61 if the lower heating circuit is dispensed with, is recirculated by pump 89 upward through the extraction vessel and back into the digester, either through the opposite opening 64 in the extraction vessel or through opening 65 for countercurrent flow through a portion of the digester between openings 65 and 63, as selected by valve 82. If it be desired to operate extraction vessel 7% at the same pressure as the portion of digester 22 opposite it, pump 81 may be omitted. However, if it be desired to operate extraction vessel 70 at a lower pressure for most efiicient gas extraction, for example, pump 81 must be utilized to repressurize the circulating liquid, in which case pump d may be replaced by a throttling valve. The continuous sweep of the recirculated liquid across the column of chips or downwardly therethrough as they are moved upward through the digester 22 by the plate 32 thoroughly scrubs the chips to remove evolved fluids therefrom such as gases, immiscible liquids, turpentine and the like and carry them into the extraction vessel 70. The rate of 7 flow of recirculating liquid must be relatively high in relation to chip movement, so that, preferably, complete extraction of chips takes, place within the swept zone between extraction openings 63, 64 or 63, 65. Too, the rate of chip reaction should be such that the chips have been thoroughly heated for by-product evolution when passing through such zone, but not to the point of reacting so as to reduce the yield of valuable by-products such as turpentine, for example. The same conditions are appropriate for removal of unwanted gases, which might tend to interfere with optimum digester operation under certain conditions if allowed to move upwardly through the digester without being removed by the extraction vessel of the present invention.

The extraction vessel 70 should be of sulflciently large suitable collector (not shown).

cross section so that the liquid flow rate therethrough is relatively low and must be of suflicient vertical height to enable eflicient separation as well as steam distillation of evolved turpentine if present by means of the steam passed into the bottom of the vessel through steam inlet '74. The inflowing steam, set at any desired predetermined rate by adjusting valve 75, bubbles upwardly through vessel 70 as at 86 heating the circulating liquid and distilling the turpentine in the liquid flowing through vessel 70. The turpentine vapor and excess steam passes outward through upper opening 76 and its valve 77 to a A thin layer of turpenti-nc or other immiscible liquid 92 will also form on the surface of the circulating liquid in said vessel, from which it may be removed through outlet 88 and valve 89. Any heavier specific gravity liquids may be removed through outlet 73 and valve 79.

It is essential that the level of the liquid, preferably as defined by interface 90, be controlled in the vessel 70 to maintain a position above the upper recirculation outlet 72 and below the vessel top outlet '76, preferably a substanti al distance therebelow for most eflicient steam distillation and removal of gases. This may be achieved by a variety of means, for example, with an unpressurized digester, it would be directly controlled by the liquid level in the digester itself. With a ressurized digester, however, since it would be difficult to achieve the desired level control simply by raising the extraction vessel to a height at which its head would balance the digester pressure, whether a steam inlet was utilized or simple boiling relied upon to produce the steam necessary for the distillation process, a position level sensor and control 78 is employed to maintain the level between predetermined limits substantially above the upper liquid outlet 72 and below the turpentine and steam or gas outlet 76 at the top of the vessel 79. With such a positive control, valve 77 is opened to relieve the pressure and carry over steam and turpentine to the collector if the level falls too low, thus allowing it to rise. On the other hand, if the level be too high, the valve will tend to close to pressurize the vessel to a greater extent and so depress the level. Normally, steam, turpentine and gas will flow continuously from valve 77 at a rate which is continuously adjusted by the level sensor and control 78, steam being fed into vessel 7i) at a constant rate, and this will be true whether the extraction vessel '70 be operated at the pressure of reaction vessel 22, or whether it be operated at a much lower pressure, either by raising it to a higher level, as mentioned above, or by utilizing a re-pressurizing pump 81 and a throttling valve or pump St) for reducing the reaction vessel pressure to the value desired in the extraction vessel.

Thus it will be seen that the invention provides novel extraction apparatus in a continuous pulper. Various modifications of the invention within the spirit thereof and the scope of the appended claims will be apparent to those skilled in the art.

What is claimed it:

1. Apparatus for continuously treating wood chips and simultaneously continuously extracting separable fluids therefrom, comprising a generally upright elongated reaction vessel having wood chip lifter means for feeding a wood chip-liquid mixture into the lower end of said reaction vessel to maintain a compacted mass of wood chips within the reaction vessel while feeding said mass upwardly through said reaction vessel and discharging treated wood chips from the upped end of said reaction vessel, said reaction vessel having liquid access openings positioned a substantial distance above the lower end of said reaction vessel, strainer means covering at least one of said openings adapted for discharging liquid through said strainer means from said reaction vessel, others of said access openings adapted for introducing liquid into said reaction vessel, an elongated extraction vessel having an upper fluidoutlet opening and upper and lower liquid openings connected to said reaction vessel through said liquid access openings for flow of liquid therei-nto, and means for circulating said liquid through said extraction vessel from said one opening through said strainer means from said reaction vessel and causing flow of said liquid within said reaction vessel from one access opening to another access opening, and level control means maintaining a discrete liquid level in said extraction vessel.

2. Apparatus as claimed in claim 1 wherein throttling means is provided for reducing the pressure of liquid passing from said reaction vessel to said extraction vessel and re-pressurizing means is provided for increasing the pressure of liquid passing from said extraction vessel to said reaction vessel.

3. Apparatus as claimed in claim 1 wherein said liquid access openings are vertically spaced for countercurrent flow of circulating fluid downwardly through said reaction vessel.

4. Apparatus as claimed in claim 1 wherein said liquid access openings are transversely spaced for liquid flow across said reaction vessel.

5. Apparatus as claimed in claim 1, further including valve means at the top of said extraction vessel at its outlet opening, said level control means operating said valve means to maintain a discrete liquid level in said extraction vessel spaced a substantial distance below the top thereof and above the uppermost liquid opening thereof.

6. Apparatus as claimed in claim 5 including means adjacent the bottom of said extraction vessel for supplying steam thereto.

7. Apparatus for continuously treating wood chips and simultaneously continuously extracting separable fluids therefrom, comprising a generally upright elongated reaction vessel having wood chip lifter means for feeding a wood chip-liquid mixture into the lower end of said reaction vessel to maintain a compacted mass of wood chips within the react-ion vessel while feeding said mass upwardly through said reaction vessel and discharging treated wood chips from the upper end of said reaction vessel, said reaction vessel having liquid access openings, strainer means covering at least one of said openings adapted for discharging liquid from said reaction vessel, others of said access openings adapted for introducing liquid into said reaction vessel, an elongated extraction vessel having an upper fluid outlet opening and upper and lower liquid openings connected to said reaction vessel through said liquid access openings for flow of liquid thereinto, means for circulating said liquid upwardly through said extraction vessel from said one opening through said strainer means from said reaction vessel and causing flow of said liquid within said reaction vessel from one access opening to another access opening, and level sensor and control means, said level control means maintaining a discrete liquid level in said extraction vessel spaced a substantial distance below the top thereof and above the uppermost liquid opening thereof connected to said reaction vessel.

8. Apparatus for continuously treating wood chips and simultaneously continuously extracting separable fluids therefrom, comprising a generally upright elongated re action vessel having wood chip lifter means for feeding a wood chip-liquid mixture into the lower end of said reaction vessel to maintain a compacted mass or wood chips within the reaction vessel while feeding said mass upwardly through said reaction vessel and discharging treated wood chips from the upper end of said reaction vessel, said reaction vessel having liquid access openings, strainer means covering at least one of said openings adapted for discharging liquid from said reaction vessel, others of said access openings adapted for introducing liquid into said reaction vessel, an elongated extraction vessel having an upper fluid outlet opening and upper and lower liquid openings connected to said reaction vessel through said liquid access openings for flow of liquid thereinto, means for circulating said liquid through said extraction vessel from said one opening through said strainer means from said reaction vessel and causing flow of said liquid within said reaction vessel from one access opening to another access opening, and level sensor and control means, said level control means maintaining a discrete liquid level in said extraction vessel spaced a substantial distance belowthe top thereof and above the uppermost liquid opening thereof connected to said reaction vessel.

9. Apparatus as claimed in claim 8 wherein throttling means is provided connected between said lower liquid opening and said digester, and re-pressurizing means is provided between said upper liquid opening and said digester, for reducing the pressure of liquid recirculated within said extraction vessel for evolution of gas therefrom.

10. Apparatus as claimed in claim 9, further including means for heating liquid within said extraction vessel.

11.v Apparatus as claimed in claim 10 wherein said lower liquid opening is connected to said digester at a point vertically spaced below the connection of said upper liquid opening.

12. Apparatus for continuously treating wood chips and simultaneously continuously extracting vapors of turpentine therefrom, comprising a generally upright elongated reaction vessel having wood chip lifter means for feeding a wood chip-liquid mixture into the lower end of said vessel to maintain a compacted mass of wood chips within the reaction vessel while feeding said mass upwardly through said vessel and discharging treated wood chips from the upper end of said vessel, said reaction vessel having liquid access openings spaced opposite one another thereacross, strainer means covering at least one of said openings adapted for discharging liquid from said reaction vessel, others of said access openings adapted for introducing liquid into said reaction vessel, an elongated extraction vessel having an upper turpentine outlet opening and upper and lower liquid openings connected to said reaction vessel through said liquid access openings for continuous flow of strained liquid thereinto through B said strainer means, means for continuously circulating liquid upwardly through said extraction vessel from said reaction vessel through said strainer means and causing flow of said liquid across said reaction vessel from one access opening to another access opening, valve means at the top of said extraction vessel at its turpentine outlet opening and level sensor and control means, said level control means operating said valve means to maintain a discrete liquid level in said extraction vessel spaced a substantial distance below the top thereof and above the uppermost liquid opening thereof and means adjacent the bottom of said extraction vessel for supplying steam thereto for steam distilling turpentine in said extraction vessel and carrying said turpentine through said turpentine outlet opening.

References Cited in the file of this patent UNITED STATES PATENTS 1,004,473 Saylor Sept. 26, 1911 1,817,129 Davies Aug. 4, 1931 2,414,062 Richter Jan. 7, 1947 2,459,570 McGregor Jan. 18, 1949 2,809,111 Durant, Oct. 8, 1957 3,007,839 Richter Nov. 7, 1961 3,061,007 Rich Oct. 30, 1962 

1. APPARATUS FOR CONTINUOUSLY TREATING WOOD CHIPS AND SIMULTANEOUSLY CONTINUOUSLY EXTRACTING SEPARABLE FLUIDS THEREFROM, COMPRISING A GENERALLY UPRIGHT ELONGATED REACTION VESSEL HAVING WOOD CHIP LIFTER MEANS FOR FEEDING A WOOD CHIP-LIQUID MIXTURE INTO THE LOWER END OF SAID REACTION VESSEL TO MAINTAIN A COMPACTED MASS OF WOOD CHIPS WITHIN THE REACTION VESSEL WHILE FEEDING SAID MASS UPWARDLY THROUGH SAID REACTION VESSEL AND DISCHARGING TREATED WOOD CHIPS FROM THE UPPED END OF SAID REACTION VESSEL, SAID REACTION VESSEL HAVING LIQUID ACCESS OPENINGS POSITIONED A SUBSTANTIAL DISTANCE ABOVE THE LOWER END OF SAID REACTION VESSEL, STRAINER MEANS COVERING AT LEAST ONE OF SAID OPENINGS ADAPTED FOR DISCHARGING LIQUID THROUGH SAID STRAINER MEANS FROM SAID REACTION VESSEL, OTHERS OF SAID ACCESS OPENINGS ADAPTED FOR INTRODUCING LIQUID INTO SAID REACTION VESSEL, AN ELONGATED EXTRACTION VESSEL HAVING AN UPPER FLUID OUTLET OPENING AND UPPER AND LOWER LIQUID OPENINGS CONNECTED TO SAID REACTION VESSEL THROUGH SAID LIQUID ACCESS OPENINGS FOR FLOW OF LIQUID THEREINTO, AND MEANS FOR CIRCULATING SAID LIQUID THROUGH SAID EXTRACTIONS VESSEL FROM SAID ONE OPENING THROUGH SAID STRAINER MEANS FROM SAID REACTION VESSEL AND CAUSING FLOW OF SAID LIQUID WITHIN SAID REACTION VESSEL FROM ONE ACCESS OPENING TO ANOTHER ACCESS OPENING, AND LEVEL CONTROL MEANS MAINTAINING A DISCRETE LIQUID LEVEL IN SAID EXTRACTION VESSEL. 